Radiation-induced Lung Injury

membrane, and are just wide enough to allow the passage of red blood cells, one cell at a time. The alveoli are lined with specialized epithelial cells termed Type I pneumocytes. Interspersed among these cells are surfactant-producing Type II pneumocytes. Within the alveolar wall, pneumocytes are separated from endothelial cells by their associated basement membranes and a potential stromal space. Where present, the stromal space may contain smooth muscle cells, pericytes, fibroblasts and collagen. In some areas the alveolar wall is reduced to thin extensions of Type I pneumocytes in close approximation with the capillaries, resulting in a very thin blood-air barrier. Capillary endothelial cells are highly sensitive to ionizing radiation and thus are critical for the development of radiation pneumonitis. Damage to endothelial cells is manifested by detachment of cells from their basement membrane, obstruction of the capillary lumen by thrombi, and interruption of the continuity of Thoracic radiation is commonly employed to treat lung, esophageal, breast and lymphoma cancers. Lung inflammation caused by radiation therapy, called radiation pneumonitis (RP), is the most common dose-limiting complication of thoracic radiation. PROTOCOLS & PRACTICES Perspectives on cancer management